Can't See Banner Ads

This may be a wierd problem because many of you might prefer not to see banner ads, but I design websites and I can't check my work. It is only the standard size ads (480x60 pixels) that don't show up. I don't even get a blank box with a small x in the upper left corner, just empty space. If I resize ads by changing one dimension by 1 pixel I can see them. I am running XP Home with Service Pack 2 on a Sony Vaio. I have the same problem with any browser (IE, Netscape, Firefox and Opera). I have contacted MS, Sony and my ISP and they all blame each other. Several months ago I did not have this problem. When I started getting it, I would just System Restore to an earlier date and it would be OK for a few days. Then System Restore would not work and I lost all my early restore points.I have tried uninstalling every program I can remember installing since the problem occured. I have run Spybot, AdAware and MS Antispyware but they don't find anything relavent.

I have run Norton Anti-Virus but it never finds any viruses. I have the latest versions of all of them.I have turned off all my popup blockers, turned off my firewall, with no difference. I design my websites with Dreamweaver and when I preview a page in IE the banners show up, but when I upload the page to a server, they are gone. I can't see banner ads on anyone else's sites either.I suspect Service Pack 2, but I haven't found a way to uninstall it.